The new Mosaic feature screen saver in 10.5 is amazing, and I wanted to have a screen capture of it. Of course, when you try to screen capture, it exits the screen saver. The way around this is to press Command-Shift first, then hit the Test button in the Screen Saver panel of the Destkop & Screen Saver System Preferences panel.

Then wait for the shot you want (still holding Command and Shift), then press 3. For some reason, this doesn't end the screen saver until you let go of Command-Shift, so you can press 3 as many times as you want.

[robg adds: This works in 10.4 and 10.5.]